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Citation:
Solis MA, Metz MA (2016) An illustrated guide to the identification of the known species of Diatraea Guilding (Lepidoptera, Crambidae, Crambinae) based on genitalia. ZooKeys 565: 73-121. doi: 10.3897/zookeys.565.6797

Abstract

The genus Diatraea Guilding is one of the most economically important groups of moths in the Western Hemisphere. The larvae are stem borers that feed on species of Poaceae, or grasses, such as sugarcane, corn, rice, and sorghum, as well as many other native grasses. Interest in this group has risen considerably since sugarcane and other grasses have been utilized and/or investigated as biofuels. This is the first modern study to treat all 41 valid described species. Most type specimens were examined and we provide a checklist with 19 new synonyms. We provide keys for the identification of most species in this genus based on morphology of the male and female genitalia and modern illustrations of male and female genitalia. We also provide an updated table of species distribution by country.

Keywords

Diatraea, sugarcane moths, Poaceae, biofuels, genitalia

Introduction

The genus Diatraea Guilding is composed of externally similar species, i.e. species cannot be identified using external characters only, and occur in the Western Hemisphere. The type species is Diatraeasaccharalis (Fabricius, 1794) (Fig. 1), a major pest of sugarcane. The literature is abundant with studies on the biology of this and other closely related species that are economically important beginning with Guilding (1828). In this paper we consider 41 distinct taxa represented by 41 valid names and 46 synonyms. Some synonyms (e.g., D.busckella Dyar & Heinrich, 1927) at one time were considered valid species or subspecies based on insignificant amounts of variation and/or locally disparate distributions. Fortunately, the morphology of the genitalia has provided excellent characters for identification for most species. This study treats the entire genus as it is currently circumscribed throughout the Western Hemisphere. We provide a table of the species distributions as is currently known (Suppl. material 1) compiled from Box (1931) and the USNM collection (National Museum of Natural History, Smithsonian Institution, Washington, DC). Absence of a country from this table may not indicate that it does not occur there; it indicates that we have not seen material of that species from that country. During the course of this study we discovered more new species and the potential for cryptic species (e.g. Joyce et al. 2014, Solis et al. 2015), but we decided to publish keys to the identification of described species due to the number of identification requests and workshop requests that were being submitted to MAS (e.g. Solis 2004, Vargas et al. 2013). We provide a key to adults of the Crambinae as modified from Munroe and Solis (1998). The Diatraea diagnosis is from an excellent study of the North American Crambinae by Landry (1995).

Figure 1.

Lateral habitus and male genitalia of Diatraeasaccharalis (Fabricius, 1794), the type species of Diatraea (modified from Solis and Metz 2011).

Over eighty species names have been associated with Diatraea or related genera since Fabricius described the type species as Phalaenasaccharalis in 1794. Early studies by Dyar and Heinrich (1927) and Box (1931) listed 39 and 48 species, respectively. More modern checklists list more, various numbers of species. Bleszynski (1967) lists 55 species, Munroe et al. (1995) lists 57 species, and Nuss et al. (2015) list 58 species. The first overview of Diatraea and related genera was in the 1927 treatment by Dyar & Heinrich. They treated the 22 known species and described 9 new species; they created entirely new species concepts. Several species names were unrecognized, that is, their only reference was a species description and not specimens. They were the first to comparatively use and illustrate the male and female genitalia using pen and ink. The last major overview of Diatraea and related genera was Box (1931). He recognized 48 species, including 10 new species. He illustrated the genitalia with black and white photos when he deemed the pen and ink illustrations deficient. Unfortunately, his photographs were often with insufficient magnification. For the first time, he provided a distribution chart by country for the 48 species. He provided a key to external characters primarily using the frons, forewing color, and venation, although he suggested that genitalia dissections be done whenever possible.

Methods

Type specimens of Diatraea species were studied to confirm identity of species. Approximately 50% of the types are located at the Natural History Museum (BMNH) in London, United Kingdom, and most of the others are located at the National Museum of Natural History (USNM) in Washington, DC, USA. Almost all of the type specimens at the USNM had been previously dissected for the study by Dyar and Heinrich (1927). Dissections of material from the Carnegie Museum of Natural History (CMNH), Pittsburgh, PA, USA, were labeled CMNH and given sequential numbers.

Genitalia preparation for identification (Clarke 1941, Robinson 1976): the abdomen is removed by pushing the abdomen up with forceps. If the metathorax is still attached to the abdomen it should be separated from the abdomen. The male or female abdomen is then placed in a vial with 10% + KOH. The vial is then placed in a beaker with boiling water. The abdomen in KOH is boiled until air bubbles can be seen in the abdomen. Alternatively, the abdomen can be left in cold 10% KOH overnight. The abdomen is then removed from the KOH and placed in water. Then a brush is used to clean the scales from the abdomen, particularly the anal area if it is a male. For males the genitalia can be removed by holding the valvae and uncus with forceps, and then pulling posteriorly at the same time that the abdomen is being held anteriorly with either the brush or the forceps. The male genitalia of Diatraea can be very sclerotized so often staining is not required to see the structures. At this point, when the genitalia is in water, the male can be identified using the key to males below. A pair of forceps can force the valvae apart or a small piece of glass can be placed on the genitalia to flatten it out to be able to see certain structures. For structure recognition in the male genitalia, two views, lateral (Fig. 1) and flattened (Fig. 2), are given and labeled.

To remove the female genitalia, the abdomen should be cut laterally the entire length and then around the abdomen between segments VI and VII. The female may have more tissues surrounding the genitalia and must be cleaned with a brush carefully. The corpus bursae varies in length and width, so it is better to examine it when it is still turgid. If slide mounted, care should be taken to not fold, tear or collapse the corpus bursae. The female apparatus is usually membranous, but may not need staining. If staining is required to see structures use a saturated solution of chlorazol black for only a few seconds. The female can then be identified using the key to females below. The genitalia can then be stored in genitalia vials with glycerin if available, or in 70% alcohol that may harden, but will also preserve, the genitalia as vouchers. Two videos are also available to view dissection techniques in great detail (Brown et al. 2009, 2011).

Terminology within the keys and the major structures of the male genitalia are as follows (Figs 1, 2): valva (e) (harpe of Dyar and Heinrich 1927), basal lobe from the costa of the valvae, juxta (anellus of Dyar and Heinrich 1927), gnathos, tegumen, lateral lobe of the tegumen (but see Landry 1995, p. 69, “a pair of extensions posterad from base of ventral margin”), vinculum, and the phallus (aedoeagus of Dyar and Heinrich 1927) that includes a vesica with a cornutus (or cornuti).

The female genitalia (Figs 27, 29) consists of the papillae anales or ovipositor, anterior and posterior apophyses, an ostium bursae (genital opening of Dyar and Heinrich 1927), ductus bursae, and corpus bursae; bursae copulatrix is the term used for the ductus bursae + corpus bursae. Associated with the corpus bursae in a few Diatraea species is a sclerotized signum or many signa that may take various forms and may be diagnostic of species. Associated with the ostium bursae are: sterigma (= ostiolar sclerites (Gaskin 1971)), sclerotized structures, sometimes very complex, surrounding the ostium bursae; lamella antevaginalis, the anterior, often the ventral, side, of the sterigma; lamella postvaginalis, the posterior, often dorsal side, of the sterigma. The section of the ductus bursae near the ostium bursae is called the antrum, and a sclerotized structure just below it, or anterior to it, if present, is called a colliculum.

Results

The adapted key below using external and tympanal characters from Munroe and Solis (1998) can aid in identifying a species as Crambinae.

Key to Crambinae in Relation to the other Subfamilies of Pyraloidea

(adapted from Munroe and Solis 1998)

1

Praecinctorium absent; tympanal case “closed” medially and open anteriorly only; tympanum and conjunctiva in the same plane

Chaetosema absent; forewing with distal part of CuP developed as a tubular vein; proboscis present, but reduced; tympanal cases reduced and widely separated; praecinctorium reduced

other Crambidae

–

Chaetosema present; forewing with CuP absent, not developed as a tubular vein; proboscis usually present and tympanal organs almost always normally developed

3

3

R2 of forewing at least closely apposed to and usually stalked with R3+4; labial palpus usually upturned, basal segment often longer than second segment; wings mostly with conspicuous pattern of transverse bands on a pale ground; larvae aquatic, rarely in damp terrestrial habitats

other Crambidae

–

R2 of forewing well separated from R3+4; labial palpus often porrect, basal segment much shorter than second segment; wings usually without conspicuous pattern of transverse bands on a pale ground; larvae usually terrestrial, sometimes stem borers in aquatic graminaceous plants

4

4

Forewing usually with weakly raised patches of black scales; cubitus of hindwing usually not pectinated with hairlike scales; lateral arms of tegumen of male genitalia about as long as uncus, little tapered ventrally; uncus of moderate length, pyriform, hoodshaped or bilobed, not obviously decurved from base to tip; gnathos with median element spikelike, sword-shaped, or digitate, straight or decurved, rarely reduced; uncus and gnathos not forming a jawlike structure, and not widely separated dorsad from valvae; valva sometimes with a ventral process but, except in Heliothela, without strong costal or medial armature; known larvae on mosses, lycopods, ferns, and roots of seed-bearing vascular plants

Scopariinae

–

Forewing without raised patches of black scales; cubitus of hindwing usually pectinated with hairlike scales, lateral arms of tegumen of male genitalia much longer than uncus or narrowed ventrally, usually both; uncus usually long, acuminate, and more or less decurved from base to tip; gnathos with lateral arms articulating at base of uncus, medial element various in shape, often rodlike or forming a dorsally directed hook; uncus and gnathos forming a jawlike structure, widely separated dorsad from valvae; valva often with strong costal process or medial armature; larvae mostly feeding at bases, roots, stems of grasses (Poaceae)

Crambinae

Diagnosis of Diatraea

In the CrambinaeDiatraea is morphologically defined by a combination of derived characters including a lack of ocelli on the head (absent or reduced in the externally similar Donacoscaptes and Xubida (B. Landry, pers. comm.)), the presence of pockets with specialized scales on the male second abdominal segment, hair tufts on the male hind tibia, in the male genitalia basal extensions of the tegumen in some or most species (Landry 1995). Landry (1995) also suggested that the shape of the female sterigma with shallow sclerotized, often spinose, depressions on each side of the ostium bursae, may be unique to Diatraea (in contrast to the externally similar Donacoscaptes and Xubida where “the setation of the female segment VIII is concentrated apico-dorsally” and “the female sterigma and segment VIII are sometimes linked by a narrow sclerotized bridge which may be single or double” (Landry 1995)). Another potentially derived structure in the male genitalia could be the lack of muscle attachments in the lateral lobes of the tegumen (Solis and Metz 2011).

Note: Described from a series of 7 specimens from Venezuela and Brazil. Box (1931: Plate III) figured two female genitalia dissections (BMNH #141 and #142) that we studied. Figured in this paper is Figure 26d that is BMNH #142 (= Box #3). Box considered the dissected female, BMNH #141, to be the last remaining syntype of Walker’s original series. The locality is unknown, but presumed by Box (1931:41-42) to be Venezuela: “The only specimen which we can to-day assert to have been included among the above, is the female type in the British Museum from Venezuela.”

Note: This appears to be a variable species based on the number of specimens available and barring numerous dissections. Despite differences in size and coloration, the male genitalia are consistent throughout with the same morphology for the uncus and gnathos, lateral process of the tegumen, and costal processes. The females, however, are not consistent. In the impersonatella form, the lamella postvaginalis has the transverse ridges at an angle so that medially they are farther from the ostium bursae than the lateral ends and the membranous area in the middle is wide and widens past the ridges forming an hourglass shape. In the moorella form it is either like the impersonatella form or has the transverse ridges completely absent and the lamella postvaginalis a large roughened patch without a wide membranous area in the middle. The pallidostricta and flavipennella (and some moorella) form females have a much rounder lamella postvaginalis that is often glabrous and the transverse ridges are arcuate. Nomenclaturally, the synonomy for this group of names is also confounded by the lack of single typification for the syntype series and that some of these species are represented by female holotypes among what seems to be variable female genitalia.

Diatraeapallidostricta Dyar, 1911: 205. Type locality: São Paulo, Brazil. Syn. n. Note: Bleszynski (1967) considered D.pallidostricta a junior synonym of Zeadiatraealineolata in the World Catalog, but this was a mistake; it was repeated in Munroe et al. (1995).

Note: Only known from two specimens, the female holotype in the USNM and a male that Box determined to be conspecific based on external characters and type locality. The male and female may not actually be conspecific.

Gnathos in lateral view more-or-less straight from base to tip, dorsal surface slightly undulate, but not arcuate, only tip with slight hook; tegumen in lateral view larger at the base than at the point of articulation with uncus/gnathos; brush of setae at tip of valva dense and long, length more than twice width of valva where brush emerges from valva (Fig. 5a, b)…

maronialis

24’

Gnathos in lateral view arcuate, middle of dorsal surface “lower” than base and tip; tegumen in lateral view more-or-less equal in width throughout length; brush of setae at tip of valva only slightly more conspicuous than rest of setae on valva, length subequal to width of valva where brush emerges from valva (Fig. 6a, b)

Uncus with ventrolateral, carinate margin constricting sharply and is not carinate just before apex of uncus, thus making apex slightly spatulate; basal costal lobe of valva capitate, posterior surface evenly rounded and lacking a depression; transition between basal costal lobe and following section of costa smooth, not notched (Fig. 16a, b)

indiginella

33’

Uncus with a ventrolateral, carinate margin that is complete, not tapered before reaching apex; basal costal lobe of valva protruding posteriorly only, not widened laterally at apex, with small depression in posterior surface; with roughened notch between base of basal costal lobe and following section of costa (Fig. 14g, h)

Denticulation of valva basal costal lobe small, lobe essentially not darkened more than rest of cuticle as a result of denticulation (Fig. 15e)

impersonatella

39’

Denticulation of valva basal costal lobe large, lobe darkened more than rest of cuticle as a result of denticulation (Fig. 13e)

busckella

Simple key to Diatraea species based on female genitalia

[The female is unknown for the following species and therefore not included in the key below: castrensis Dyar & Heinrich, 1927; schausella Dyar & Heinrich, 1927. We did not have female specimens on hand of ragonoti Box, 1948 and suffusella Box, 1931.]

Corpus bursae completely membranous, at most with areas of darkened cuticle

3

2 (1)

Lamella antevaginalis hardened and darkened, appearing as a medially-bisected plate that protrudes posteriorly over the genital opening; corpus bursae with a ring of sclerotized flattened plates (Fig. 22d)

strigipennella

2’

Lamella antevaginalis membranous, possibly sclerotized as much as sternites, but not dark or protruding over the genital opening; corpus bursae with opposite patches of sclerotized teethlike spines (Fig. 21c)

lentistrialis

3 (1’)

Sternite VIII with a broad, transverse “pocket” mostly concealing ostium bursae; lamella antevaginalis composed of a pair of hardened, posteriorly projecting extensions that may cover the genital opening or surround it laterally; lamella postvaginalis with lateral areas of wrinkled and/or densely setose cuticle contrasting strikingly with medial area that is smooth and glabrous; or if lamella postvaginalis immediately posterad ostium bursae smooth and concave then with a pair of densely setose transverse ridges posterad concavity that project ventrally (saccharalis group) (Fig. 28a)

4

3’

Sternite VIII with ventral surface continuous with ostium and membranous never forming a transverse pocket concealing ostium; or if lamella antevaginalis and/or lamella postvaginalis varously sclerotized and ostium concealed then without contrasting lateral areas of roughened or densely setose cuticle and a pair of densely setose transverse ridges posterad

12

4 (3)

Corpus bursae more than 5× longer than wide; corpus bursae shape cylindrical, more or less parallel sided (Fig. 26c)

guatemalella

4’

Length of corpus bursae variable, but if longer than wide then less than 5× longer than wide; corpus bursae shape variable, but usually irregular to ovate

Ductus bursae more or less smooth, lightly darkened except for contrasting colliculum at junction with corpus bursae that is considerably darker; corpus bursae without any darkened areas at base, completely membranous (Fig. 27a)

Corpus bursae length 2× greater than width or less, irregularly shaped or ovate, width at middle appearing to contribute to overall shape of corpus rather than as lateral expansions; posteriorly projecting extensions of lamella antevaginalis enlarged and conspicuous, middle membranous area much narrower

Antrum with heavy sclerotization in the shape of a yoke, narrower at dorsal margin of ostium bursae, widening laterally and descending down antrum, lateral edges folded inward forming a trough (Fig. 20b)

brunnescens

15’

Antrum variously sclerotized, but sclerotization not shaped like a yoke or lateral edges folded into a trough

16

16 (15’)

Antrum and ductus bursae only lightly sclerotized or not at all, colliculum not evident; union of ductus bursae and corpus bursae smooth, not constricted, so that beginning of corpus is indistinct (Fig. 26b)

dyari

16’

Antrum and ductus bursae with some sclerotization and colliculum usually present; if sclerotization of membrane light or indistinct then terminus of ductus bursae and beginning of corpus bursae always obvious

17

17 (16’)

Terminal end of ductus bursae with a spherical, membranous expansion that is 2× wider than ductus bursae before pinching to opening of corpus bursae (Fig. 22b)

myersi

17’

Ductus bursae with varying shapes and widths, but never with a large, spherical expansion before the opening of the corpus bursae

18

18 (17’)

Corpus bursae medially wider due to presence of shallow lateral pockets on each side about midway, not simply oval-shaped

19

18’

Corpus bursae oval shaped, without shallow lateral pockets on each side

Acknowledgments

We would like to thank Geoff Martin, Michael Shaffer†, and Kevin Tuck (retired) at the Natural History Museum, London (NHM) for access to the Pyraloidea collection, loan of Diatraea type specimens, and especially Geoff Martin for providing much needed information at the very last minute. John Rawlins at the Carnegie Natural History Museum (CMNH) provided access to the Pyraloidea collection that provided specimens of uncommon species, and some of which are figured. Over the years many collaborators, including those below, kept MAS working on Diatraea by either collecting and/or sending specimens some of which were used for photographs, and/or organizing workshops: Mexico: Luis Rodríguez del Bosque and G. Vejar Cota, INIFAP; Colombia: Luis Antonio Gómez and Germán Vargas, Cenicaña; Ana Elizabeth Diaz, CORPOICA; El Salvador: Leopoldo Serrano C. and Miguel Semeño C., University of El Salvador; Andrea Joyce, University of California Merced; Costa Rica: Daniel Janzen, Winnie Hallwachs, Eugenie Phillips, Bo Sullivan; Venezuela: J. B. Heppner, McGuire Center for Lepidoptera and Biodiversity; Brazil: Vitor O. Becker; Guatemala: Pedro Rendon, APHIS; and in the United States: Andrea Joyce; T.L. Springer, ARS; Donald Krizek, ARS (retired); Don Riley, APHIS (retired). We thank Bernard Landry and another anonymous reviewer for very helpful comments on the manuscript. Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the USDA. USDA is an equal opportunity provider and employer.

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